Temperature measurement

ABSTRACT

A reheating furnace for slabs or billets is provided with at least one temperature measuring device having an upwardly directed radiation receiving surface provided by a plate located at the upper end of a cyclindrical housing. Substantial thermal insulation is provided around the housing and in use the radiation receiving surface of the plate is disposed closely adjacent to and facing the underside of a slab being heated, the thermal insulation shielding the surface from ambient radiation whereby radiation is received by the surface substantially solely from the under surface of the slab.

1 United States Patent 1191 [111 3,806,309 Laws et al. Apr. 23, 1974 [5TEMPERATURE MEASUREMENT 3,539,100 11/1970 Gentry 236/15 1; I 1 WillemRobert Laws, Worcester iSZZiZZ $335 filiiiiiiiii: 432/50 Park; HerbertRaymond McChesney, St. Albans; Frank Michael Salter, Coulsdon, all ofPrimary Examiner-John J. Camby England Attorney, Agent, or Firm- Bacon &Thomas; Jesse B. [73] Assignee: The British Iron and Steel ResearchGrove Jerry Thlebeau 1 1 j Association, London, England 22 Filed: 12,1972 [57] ABSTRACT [21] Appl. No.2 314,392 A reheating furnace for slabsor billets is provided with at least one temperature measuring devicehaving an upwardly directed radiation receiving surface pro- [30] Forms"Application grionty D vided by a plate located at the upper end of acyclin- Dec. 22, 1971 Great Britam 59655/71 drical housing Substantialthermal insulation is vided around the housing and in use the radiationre- [52] US. CL", 432/50,:36/15 B, 432/126 caving surface f plate idisposed closely adja; [5]] Int. Cl. F27b 9/40 cent to d facing theunderside of Slab being [58] new of Search 432/121, 2 50; heated, thethermal insulation shielding the surface 1 236/15 B from ambientradiation whereby radiation is received a I by the surface substantiallysolely from the under sur- 1 [56] References Cited face of the Slab 1UNITED STATES PATENTS y 3,447,745 6/1969 Perrine et al 236/15 B 6Claims, 3 Drawing Figures 1 TEMPERATURE MEASUREMENT To control furnacesfor reheating stock such as metal slabs or billets requires a knowledgeof the stock temperature. Attempts to do this have met many problemssome associated with the very high temperature of gases in the furnacee.g., more than l,300C. Proposals to use radiation pyrometers formeasuring stock temperature have not been successful because, amongother reasons, the radiation from the flames and furnace walls arereflected from the slab surface and slabs are cool relative to thefurnace walls at the commencement of heating.

According to the present invention there is provided a furnace forheating metal slabs including means for i supporting metal slabs duringtheir movement through the furnace, a plurality of heat sources locatedwithin the furnace and at least one temperature measuring device havingan upwardly directed radiation receiving surface disposed at a levelbelow the level of the top of the supporting means; said device being soconstructed and arranged that in use the radiationreceiving surface isdisposed closely adjacent and facing the underside of a slab. beingheated, said surface being substantially shielded from ambient radiationwithin the furnace whereby radiation is received on said surfacesubstantially solely from the under surface of the slab.

The measuring device according to the invention can be spaced a smalldistance from the slab so that background radiation is eliminated. Thespacing can for example be between 1 and 3 centimetres. By disposingthedevice so that it faces the underside of the stock, variations instock size 'do not affect the spacing of the stock from the device, aproblem which has been encountered by many previously proposed devices.Since the surface is close to the slabs any scale which falls on to thesurface will be removed as the slabs are pushed along over the surface.

The furnace can be on any type of furnace but is preferably a pusherfurnace in which the supporting means consists of skids extending alongthe length of the furnace supported on cross members. The temperaturemeasuring device can be mounted on a supporting system independent ofthe skid support system or can be mounted on a cross member that alsosupports the skids. The device can be rigidly mounted but it is alsopossible to have the radiation receiving surface movable so that it canbe deflected by bent slabs. For example the device can be pivoted andspring urged. There are preferably a number of temperature measuringdevices spaced along the length of the furnace. The furnace can be of atype in which all the burners are directed in the same sense or of atype in which the burners in the preheat zone areopposed to the burnersin the soak zone.

The temperature measuring device preferably includes a housing, a plateforming said radiation receiving surface thermally insulated from thehousing, and a thermocouple connected to the plate, the leads for thethermocouple passing through said housing. Preferably the housing issurrounded by insulating material presenting a generally flat surfacegenerally level with the radiation receiving surface. The leads can passthrough the furnace in close proximity with the cross member which maybe suitably cooled. One of the advantages of the invention is that noseparate holes have to be provided in the furnace walls for the deviceto pass through.

In the accompanying drawings:

FIG. 1 shows a longitudinal cross section through one example of a slabreheating furnace with temperature measuring devices in accordance withthe invention,

FIG. 2 is a section on the line II II of FIG. I and FIG. 3 is a crosssection through the temperature measuring devices shown in FIGS. 1 and2. r

A' slab reheating pusher furnace 2 has two heating zones 4 and 6 with awaste gas offtake 8 between them. The zone 4 is longer than the zone 6and each zone is heated by burners 10 in the end walls of the zones sothat the flames of the burners 10 in zone 4 are opposed to the flames ofthe burnersl0 in zone 6. Water cooled skids 12 extend along the lengthof the furnace 2 for supporting slabs 14 to be heated. The burners 10are disposed above and below the skids 12 so that the slabs are heatedfrom below as well as above. The skids 12 are supported on cross members16 consisting of water cooled pipes which in turn are supported on watercooled upright members 18.

Slabs 14 to be heated are introduced through an entrance 20 and arepushed through the furnace 2 by successively introduced slabs until theslabs are discharged through discharge chute 22.

The skids 12 consist of water cooled pipe 24 supported on which is arail 27 on which the slabs 14 bear.

A number of temperature measuring devices 26 are spaced along the lengthof the furnace 2 mounted on cross members 16. Each device 26 includes acylindrical housing 28 connected to the cross member 16 by a sleeve 30to which it is welded after the desired height of the device has beendetermined. The housing 28 is surrounded with thermal insulation 32. Atthe upper end of the-housing 28 there is a plate 34 forming a generallyflat radiation receiving surface 36 thermally insulated from the housing28 by thermally insulating material 38. A thermocouple 40 passesinto theplate 34. The plate 34 is held in position by a cylindrical member 48. Alead for the thermocouple, passes through a plug 46 in the member 48 atthe bottom end of the housing 28 and passes along the cross member 16.The lead 50 is strapped to the cross member 16 and is covered withthermal insulation 52. The inside of the member 48 is filled withinsulating material.

The upper surface 36 of plate 34 is arranged to be spaced between 1 to 3centimetres below the level of the top of the rails 27 that support theslabs l4 and hence the same distance below the bottom of the slabs 14.The upper surface. 42 of the insulation material 32 is level with thesurface 36 and offers sufficient blockage such that practically noradiation reaches the surface 36 except radiation from the slabs 14. Thethermocouple 40 will therefore register a reading which is remeasuringdevice 26, the slabs 14, are in turn, shielded from the furnace heat.This is generally undesirable,

therefore the size of insulation chosen must be a compromise.

We claim:

A metal slab reheating furnace, comprising: means for supporting metalslabs during their movement through the furnace; heat sources within thefurnace and at least one temperature measuring device comprising ahousing having an open upper end; a plate providing an upwardly directedradiation receiving surface disposed in the open upper end of saidhousing at a level below the level of the top of said supporting tion isreceived on said surface substantially solely from the under surface ofthe slab.

2. A furnace as claimed in claim 1 wherein said thermal insulation meanssurround the exterior side wall surface of said housing.

3. A furnace as claimed in claim 2 wherein said thermal insulation meansis disposed level with said radiation receiving surface of said plate.

4. A furnace as claimed in claim 3 wherein said housing comprises ahollow cylindrical member packed with thermally insulating material.

5. A furnace as claimed in claim 1 wherein a plurality of said heatsources are disposed above and below the supporting means.

6. A furnace as claimed in claim 1 wherein said radiation receivingsurface is disposed at a level between 1 and 3 centimetres below thelevel of the top-of the supporting means.

1. A metal slab reheating furnace, comprising: means for supportingmetal slabs during their movement through the furnace; heat sourceswithin the furnace and at least one temperature measuring devicecomprising a housing having an open upper end; a plate providing anupwardly directed radiation receiving surface disposed at a level belowthe level of the top of said supporting means, said plate beingthermally insulated from said housing; and thermal insulation meanssurrounding the perimeter of said surface, said surface being disposedin use, closely adjacent to and facing the underside of a slab beingheated and being substantially shielded from ambient radiation withinthe furnace by said thermal insulation means whereby radiation isreceived on said surface substantially solely from the under surface ofthe slab.
 2. A furnace as claimed in claim 1 wherein said thermalinsulation means surround the exterior side wall surface of saidhousing.
 3. A furnace as claimed in claim 2 wherein said thermalinsulation means is disposed level with said radiation receiving surfaceof said plate.
 4. A furnace as claimed in claim 3 wherein said housingcomprises a hollow cylindrical member packed with thermally insulatingmaterial.
 5. A furnace as claimed in claim 1 wherein a plurality of saidheat sources are disposed above and below the supporting means.
 6. Afurnace as claimed in claim 1 wherein said radiation receiving surfaceis disposed at a level between 1 and 3 centimetres below the level ofthe top of the supporting means.